A:基因、染色体、细胞
B:细胞、物种、生物圈
C:基因、物种、生态系统
D:物种、种群、生态系统
— Liu Xiang won the 110-meter hurdling gold at the 11th National Games again.
— He is always a super star in my heart. Congratulations to him.
已知函数f(x)=x2+(lga+2)x+lgb满足f(﹣1)=﹣2且对于任意x∈R,恒有f(x)≥2x成立.
(1)求实数a,b的值;
(2)解不等式f(x)<x+5.
如图,已知AB∥CD∥EF,AD:AF=3:5,BE=10,那么BC的长等于____.